Tungsten nanowire based hyperbolic metamaterial emitters for near-field thermophotovoltaic applications

Jui Yung Chang, Yue Yang, Liping Wang

Research output: Contribution to journalArticle

46 Citations (Scopus)

Abstract

Recently, near-field radiative heat transfer enhancement across nanometer vacuum gaps has been intensively studied between two hyperbolic metamaterials (HMMs) due to unlimited wavevectors and high photonic density of state. In this work, we theoretically analyze the energy conversion performance of a thermophotovoltaic (TPV) cell made of In<inf>0.2</inf>Ga<inf>0.8</inf>Sb when paired with a HMM emitter composed of tungsten nanowire arrays embedded in Al<inf>2</inf>O<inf>3</inf> host at nanometer vacuum gaps. Fluctuational electrodynamics integrated with effective medium theory and anisotropic thin-film optics is used to calculate the near-field radiative heat transfer. It is found that the spectral radiative energy is enhanced by the epsilon-near-pole and hyperbolic modes at different polarizations. As a result, the power output from a semi-infinite TPV cell is improved by 2.15 times with the nanowire HMM emitter over that with a plain tungsten emitter at a vacuum gap of 20 nm. Moreover, by using a thin TPV cell with 10 μm thickness, the conversion efficiency can be greatly improved from 17.7% to 31.1% without affecting the power generation, due to the total internal reflection occurring at the bottom cell interface that minimizes the sub-bandgap spectral radiative energy. Furthermore, the effects of a TPV cell and a nanowire emitter with finite thicknesses are also studied. The result shows that the maximum efficiency of 31.8% is achieved with an optimal cell thickness of 3 μm while the nanowire HMM emitter should be thick enough to be opaque. The fundamental understanding and insights obtained here will facilitate the design and application of novel materials in enhancing near-field TPV energy conversion.

Original languageEnglish (US)
Pages (from-to)237-247
Number of pages11
JournalInternational Journal of Heat and Mass Transfer
Volume87
DOIs
StatePublished - Aug 1 2015

Fingerprint

Tungsten
Metamaterials
Nanowires
near fields
tungsten
emitters
nanowires
Vacuum
cells
Energy conversion
radiative heat transfer
energy conversion
vacuum
Heat transfer
Electrodynamics
Photonics
Conversion efficiency
Power generation
Poles
Optics

Keywords

  • Effective medium
  • Hyperbolic metamaterial
  • Near-field radiation
  • Thermophotovoltaic
  • Thin films

ASJC Scopus subject areas

  • Mechanical Engineering
  • Condensed Matter Physics
  • Fluid Flow and Transfer Processes

Cite this

Tungsten nanowire based hyperbolic metamaterial emitters for near-field thermophotovoltaic applications. / Chang, Jui Yung; Yang, Yue; Wang, Liping.

In: International Journal of Heat and Mass Transfer, Vol. 87, 01.08.2015, p. 237-247.

Research output: Contribution to journalArticle

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abstract = "Recently, near-field radiative heat transfer enhancement across nanometer vacuum gaps has been intensively studied between two hyperbolic metamaterials (HMMs) due to unlimited wavevectors and high photonic density of state. In this work, we theoretically analyze the energy conversion performance of a thermophotovoltaic (TPV) cell made of In0.2Ga0.8Sb when paired with a HMM emitter composed of tungsten nanowire arrays embedded in Al2O3 host at nanometer vacuum gaps. Fluctuational electrodynamics integrated with effective medium theory and anisotropic thin-film optics is used to calculate the near-field radiative heat transfer. It is found that the spectral radiative energy is enhanced by the epsilon-near-pole and hyperbolic modes at different polarizations. As a result, the power output from a semi-infinite TPV cell is improved by 2.15 times with the nanowire HMM emitter over that with a plain tungsten emitter at a vacuum gap of 20 nm. Moreover, by using a thin TPV cell with 10 μm thickness, the conversion efficiency can be greatly improved from 17.7{\%} to 31.1{\%} without affecting the power generation, due to the total internal reflection occurring at the bottom cell interface that minimizes the sub-bandgap spectral radiative energy. Furthermore, the effects of a TPV cell and a nanowire emitter with finite thicknesses are also studied. The result shows that the maximum efficiency of 31.8{\%} is achieved with an optimal cell thickness of 3 μm while the nanowire HMM emitter should be thick enough to be opaque. The fundamental understanding and insights obtained here will facilitate the design and application of novel materials in enhancing near-field TPV energy conversion.",
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